The present invention relates to protocol testing, and more particularly to a method and a protocol tester for decoding data encoded in accordance with a protocol description for the performance of a measurement task.
Particularly in protocol measurement technology, the encoding, decoding and analysis of digital data occupies a central role, with so-called protocol data units being examined by computer software and the information contained therein being extracted. In this context, FIG. 1 shows a procedure known from prior art, in which an interpretative decoder 10 reads a general protocol description 12 and, based on the protocol description, decodes encoded data 14 also read in, and makes the data available as decoded information 16 to a processing device 20. The general protocol description is firm, suited for a plurality of measurement tasks and describes the encoded data, as a maximum, exactly down to each bit. The general protocol description preferably includes information on the meaning of the bits, the names of bit groups, the format of the presentation, for example a string, hexadecimal or binary, and on the formation of summaries in the form of parameters or messages. In contrast to firm decoding routines, which exist unchangeably for certain protocols, interpretative decoding routines, i.e. decoders with an interpreter, have the advantage that the very same hardware can be adapted easily to different protocols by loading the corresponding general protocol description of the associated protocol. Tree-structured protocol descriptions, however, lead to a high storage demand for a reduced calculation expense, while linear protocol descriptions lead to an increased calculation expense for a reduced storage demand.
There is also the possibility to manually program protocol descriptions for certain repetitive measurement tasks, the disadvantage being that the manually programmed protocol descriptions are designed for a certain measurement task and are therefore already no longer suitable for performing a slightly modified measurement task. In particular, it proves awkward and time-consuming, depending on the measurement task to be resolved, to select and load into the decoder device a suitable protocol description programmed manually in a reduced manner. In order to be able to perform any measurement tasks, it is therefore necessary, in the prior art, to work with the general protocol description which, regardless of whether it shows a linear structure or a tree structure, leads to a high calculation expense for the decoding process.
FIG. 2 shows elements of another protocol tester known from the prior art, the same reference signs being used in the figures for the same or for comparable elements—this applies to all figures. For the protocol tester shown in FIG. 2, the decoder 10 has a downstream filter 18, the decoder 10 transmitting on the one hand decoded data to the filter, and on the other hand information for filter adjustment. In filter 18 data not required, i.e., data which fail to meet at least one filter condition, are discarded. The data which meet the at least one filter condition are made available as decoded information 16 to the processing device 20.
Note that the decoder executes the protocol description, regardless of whether a protocol element, which does not fulfil the at least one filter condition, has already been decoded and has to be taken as a indication that a whole series of subsequent decoding depending thereon are no longer necessary. This means that certain data may be excluded from further decoding because they are of no importance for the present measurement task, which in turn means that, in the prior art, the decoding process is continued and hence the calculation expense increased unnecessarily, even though it is not really required.
What is desired is a generic method and a generic protocol tester that performs a plurality of measurement tasks at a low expense of time and calculation.